Why does gparted insert 1 or 2 MiB unallocated gaps when moving partitions?

Question

Ok, so this is my starting state in gparted:

First I move the /dev/sda6 partition, which is exactly 30 GB in size, to the right - set with "Align to: MiB", dialog says "Free Space following: 0 MiB":

... but in the end, I get 1 MiB at end instead:

Then I try to the /dev/sda5 partition, exactly 20 GB in size, to the right - set with "Align to: MiB", dialog again says "Free Space following: 0 MiB":

... but no: this time I get 2 MiB gap between /dev/sda5 and /dev/sda6:

This second, 2 MiB gap I find very surprising, especially since both partitions have exact GiB size, so MiB alignment should not be a problem.

And in fact, if I do some more Move operations, I can get sda5 and sda6 next to each other without a gap. But why do unnecessary addtional moves, just do avoid a gap which shouldn't have been there in the first place?

So, why does gparted insert these gaps, and is there a way to tell it not to insert these gaps?

Answer 1

Partitions can be aligned to the physical boundaries of hard drive cylinders. This alignment can sometimes create small amounts of unallocated space between partitions. The only setting in gparted to change this is the "align to" method. This setting can be found in the Resize/Move sub setting.

Choices are Align to:

MiB - default
Cylinder
None

There is a lot of math that goes into alignment choices for best performance. One could search for these terms and spend hours learning about this.